I am a brand new top bar beekeeper and I can't seem to find a consensus as to what kind of bottom I should have. There seem to be a lot of varroa on the bottom of my hive right now and since I'm getting more bees for my 2nd hive this week I thought now would be a good time to change things up.

What are your experiences with a mesh bottom. We live in South Carolina so the summers are very hot and humid and winters very mild (temps in the 40's-50's)

Just got back from a natural beekeeping weekend taught by Phil and we talked quite a lot about the ecofloor.
http://www.youtube.com/watch?v=SWB-pdlqeFQ
My next hive will have this and I am going to see if I can retrofit it to the hives I have with mesh floors. Typical really, the mesh was the most expensive part of the hive and as it turns out I don't need it

I noted over the last winters that with the solid floor in place that water pooled on the botton board so i kept a close eye on this as i did not want too much condensation forming in the hive.
This sump would solve that issue over winter, much like the Warre top quilt takes the condensation.

I live in Georgia, on the border with South Carolina (in the CSRA). I started out with screened bottoms in 2010. I concluded that with our heat and humidity, it was too much ventilation and the bees couldn't control the hive climate very well, and it also allowed hive beetles to enter and leave at will. I ended up removing the screen and closing up the bottom. Since last September, I've been trying a new bottom board with screw-in bottle traps/bee feeders. So far it's working well to capture the beetles, ants, and even some varroa while keeping the hive well sealed. A bait hive with this design just attracted a swarm, so they clearly don't disapprove of it.

For my new hives and retro fitting to old hives the Ecofloor is definitely the way to go for me.
I like the ideas behind the flora and fauna balance in a hive BUT even if all that is rubbish (I withhold judgement on this ) the advantages of this floor for increased temperature and moisture control within the hive are invaluable. It provides an outlet for excessive water when required, but will humidify the air when excessively dry. It provides insulation to the hive from extreme of external heat and cold. It would also works as a reservoir for heat, hive scent, and moisture releasing it back into the hive after you have let it out during a hive inspection. It is essentially a "buffer" resisting any change within the hive environment, thus once the bees have set that environment it will help it be maintained meaning the bees don't have to work so hard to regain it. Not sure how this will work for SHB etc but for me in the UK right now there isn't a better choice for any hive, not just kTBHs.

As the saying goes, all beekeeping is local. It might be great in the UK, but I don't think it will work here in the deep South. I built two hives with the detachable eco floor and ended up taking them off. Small hive beetles need to be hounded into traps by the bees, and the eco floor offers too many hiding places for them. Also, in our region we have the American cockroach, which will move into any space where they can safely find shelter.

Being someone else who lives in this "summer-steamy southern-US State" ... (although, huh?!, I had my electricblanket turned-on again(!) last night!) ... I personally think that "wire-mesh floors" are probably not such a good idea, since I have never seen a tree or a barn or any eaves of a house that actually sported such a well-intentioned "feature." To my way of thinking, it would render temperature-control within the hive largely impossible. Since we have ambient-air temperatures from 100ºF to as (absurdly, this year...) low as 9ºF, that's a gigantic range. (And yet, at least some of our bees survived it, in their rough-made closed boxes.)

Each time that I peek inside one of my hTBH's, I find that the bottoms are generally quite tidy. Therefore, I must conclude that, whatever might fall down there, the bees carry it out on their own and discard it. Works for me.

Conserving wild bees

Research suggests that bumble bee boxes have a very low success rate in actually attracting bees into them. We find that if you create an environment where first of all you can attract mice inside, such as a pile of stones, a drystone wall, paving slabs with intentionally made cavities underneath, this will increase the success rate.

Most bumble bee species need a dry space about the size a football, with a narrow entrance tunnel approximately 2cm in diameter and 20 cm long. Most species nest underground along the base of a linear feature such as a hedge or wall. Sites need to be sheltered and out of direct sunlight.